In the context of stringent legal regulations regarding the harmful emissions emitted by motor vehicles, an important measure is to keep to a low level harmful emissions produced in the respective cylinder of the internal combustion engine during combustion of the air/fuel mixture. A further measure is also to use exhaust gas after-treatment systems in internal combustion engines, which systems convert the harmful emissions generated during the combustion process of the air/fuel mixture in the respective cylinders into harmless substances. For this purpose exhaust gas catalytic converters which convert carbon monoxide, hydrocarbon and nitrogen oxides into harmless substances are used.
Both the specified influencing of the production of harmful emissions during combustion, and the conversion of harmful components with high efficiency by means of an exhaust gas catalytic converter, presuppose a very precisely adjusted air/fuel ratio in the respective cylinder.
Especially in conjunction with an arrangement of exhaust gas catalytic converters increasingly close to the engine, and in view of correspondingly specific legal regulations in individual countries, precise cylinder-individual adjustment of the air/fuel ratio is also increasingly important, since the individual exhaust gas packets mix relatively poorly because of the short mixing distance.
Increasingly strict legal regulations regarding the emission of limited pollutants make it necessary to allow small tolerance in the air/fuel ratio between the individual cylinders. Very uneven distribution and an absence of compensation lead to significant deterioration in emissions and even to detectable problems of drivability.
Furthermore, there are legal regulations for detecting cylinder-selective uneven distribution in the air/fuel ratio, which leads to exceeding of the prescribed limit values for emissions, in a progressively increasing proportion of vehicles in relation to the vehicle fleets of the respective producer.
For the purpose of precise cylinder-individual adjustment of the air/fuel ratio in the respective combustion chambers of the respective cylinders, it is known from DE 10 2004 004 291 B3 to utilize cylinder-individual lambda control, by means of which the individual deviations of the respective cylinder-individual air/fuel ratios with respect to a mean air/fuel ratio are to be minimized. A measurement signal of an exhaust gas probe arranged in an exhaust gas tract, which signal is characteristic of the air/fuel ratio in the respective cylinder, is detected at a predefined crankshaft angle in relation to a reference position of the piston of the respective cylinder and is assigned to the respective cylinder. By means of the cylinder-individual lambda controller, there is produced a manipulated variable for influencing the air/fuel ratio in the respective cylinder as a function of the measurement signal generated for the respective cylinder. The predefined crankshaft angle is adapted as a function of an instability criterion of the controller.
A cylinder-individual lambda control, in which a first and a second adaptation value are determined for different temperature ranges as a function of a respective controller value of the cylinder-individual lambda control, is known also from DE 10 2005 009 101 B3.